Bedridden patients who have to maintain a substantially motionless position for prolonged periods of time develop bedsores on the skin. These sores, referred to in medical terms as Decubitus Ulcers, are painful, hard to heal, and create conditions for further infection. Ulcer formations of this type are produced in most cases because the pressure exerted upon the skin surfaces under the body prominences of the patient which bear most of the weight of the patient when the body of the patient presses against the ordinary mattress or other body support, thereby obstructing the circulation of blood in the capillaries directly under these surfaces.
It is known that large, very deep water filled containers (waterbeds) of large size and weight permit the patient to float freely in such a manner that the pressures exerted upon the surface of the patient's body are distributed uniformly over the entire body, thus eliminating regions of high pressure under the bony prominences whereby the ulcers do not form. These large waterbeds are covered with a top plastic sheet free of tension. The patient, placed upon this sheet, does not get wet but effectively floats deep in water. However, waterbeds of such depth are much too large and too costly for general use.
When the depth and the size of the waterbed are both reduced to more convenient and smaller dimensions, as is done with the light weight water flotation mattresses, the upper surface of the mattress upon which the body is placed is subjected to a tension or shearing force which produces undue pressure against the skin, in particular under the bony prominences. The patient does not float in the same manner as in a waterbed because the body is supported by a combination of buoyancy force and the stress forces in the upper plastic sheet supporting the body. In the ideal situation using a water bed, the downwardly directed weight of the patient's body at any point along the body is counterbalanced by a force directed vertically upward by the buoyancy forces of water alone. The plastic sheet in such a case under the body of the patient and above the water is free to adjust to the contour of the patient causing no pressure whatsoever. Such an arrangement provides the best conditions for prevention of bedsores. However, when the sheet is not free to adjust, as in the case of a small light weight water mattress, the body supporting area is reduced, the depth is decreased, and most of the counterbalancing, body supporting force is derived from the tension in the top sheet of the mattress. As the surface is depressed in accordance with the body contour and weight of the patient, unequal forces are transmitted via the surface tension of the mattress. As a result regions of higher pressure are created, mainly under the body prominences which press against the underlying capillaries, and blood circulation can be obstructed as previously described.
Another type of small size mattress has been developed to deal with the problems of bedsores formation. This type of mattress is adapted to be filled with air. The whole surface of the mattress is divided in small chambers, or regions, tied together in two side by side groups. When one of the groups is inflated, the other is deflated, providing at all times an area for the body that is not resting on the mattress, but is completely relieved from pressure. Adjacent cells are alternatively inflated and deflated producing a massaging action.
Such air mattresses are not as effective as water filled mattresses in inhibiting ulcer formation.
This inferior performance is inherent in the geometry because the air pressure in the inflated region is twice as high as it would be if the entire mattress were to be completely inflated. The massaging action ameliorates but does not fully eliminate the adverse effects of localized high pressures.
The present invention is directed toward a new type of body support mattress that can be used with water or air alike. It is small in size, relatively light weight and, when air filled, can operate with considerably less air pressure than conventional air filled massaging mattresses, and yet provide excellent minimal support pressure. When filled with water, it is characterized by greatly reduced shearing stress, as compared to presently used light weight water flotation mattresses.